Since GaN-based light emitting diodes were first developed, GaN-based LEDs have been used for various applications including natural color LED displays, LED traffic signboards, white LEDs, and the like.
Generally, a GaN-based light emitting diode is formed by growing epitaxial layers on a substrate such as a sapphire substrate, and includes an N-type semiconductor layer, a P-type semiconductor layer and an active layer interposed therebetween. In addition, an n-electrode pad is formed on the N-type semiconductor layer and a p-electrode pad is formed on the P-type semiconductor layer. The light emitting diode is connected to an external power source through the electrode pads and driven thereby. In this case, current flows from the p-electrode pad to the n-electrode pad through the semiconductor layers.
On the other hand, a flip-chip type light emitting diode is used to prevent light loss due to the p-electrode pad while improving heat dissipation efficiency, and various electrode structures are proposed to promote current spreading in a large area flip-chip type light emitting diode. Examples are disclosed in U.S. Pat. No. 6,486,499. For example, a reflective electrode is formed on the P-type semiconductor layer, and extension legs are formed on a region of the N-type semiconductor layer, which is exposed by etching the P-type semiconductor layer and the active layer, to facilitate current spreading.
The reflective electrode formed on the P-type semiconductor layer reflects light generated from the active layer to improve light extraction efficiency and helps current spreading in the P-type semiconductor layer. On the other hand, the extension legs connected to the N-type semiconductor layer help current spreading in the N-type semiconductor layer to allow uniform generation of light in a wide active region. Particularly, a light emitting diode having a large area of about 1 mm2 and used for high power output requires current spreading not only in the P-type semiconductor layer but also in the N-type semiconductor layer.